1. Field of the Invention
This invention relates to a method suitable for designing an optical system.
2. Introduction to the Invention
I am working on the design of optical systems of the type shown in FIG. 1. Here, an optical system 10 includes a mirror 12, supported from a mirror mount 14, by way of a flexure 16.
It is known that one important design parameter for an optical system like that of FIG. 1, is the coefficient of thermal expansion (CTE), designated by the Greek symbol .alpha.. The CTE may be expressed by a well-known equation (1): ##EQU1## where L=length of a workpiece having a uniform thermal strain (e.g., the workpiece being the mirror 12, the mirror mount 14, or the flexure 16); and
.DELTA.L=a linear deformation of the workpiece due to a change in temperature of .DELTA.T.degree.. PA0 (1) constructing a first triangle derived from the optical system in its first temperature state, and comprising PA0 (2) constructing a second triangle derived from the optical system in its second temperature state, and comprising PA0 (3) establishing a similarity of the first and second triangles.
It is important to know the coefficient of thermal expansion, for example, when the workpiece is part of a statically indeterminate system. Here, expansion or contraction of the workpiece, induced by a change of temperature, may be inhibited or entirely prevented in certain directions. This, in turn, may cause significant distortions in the system, which distortions may have to be investigated by way of the coefficient of thermal expansion, and subsequently accommodated by the system.
For example, with reference to FIG. 1, expansion or contraction of the mirror 12, the mirror mount 14, and/or the flexure 16, induced by a change of temperature .DELTA.T, may cause significant distortions in the mirror 12, and thus vitiate its optical characteristics, for example, that of sharply focusing a radiation beam.